U.S. patent application number 14/181088 was filed with the patent office on 2014-06-12 for phosphor and led placement for white led-based lamps.
This patent application is currently assigned to MARVELL WORLD TRADE LTD.. The applicant listed for this patent is MARVELL WORLD TRADE LTD.. Invention is credited to RAVISHANKER KRISHNAMOORTHY, Sehat Sutardja.
Application Number | 20140159596 14/181088 |
Document ID | / |
Family ID | 48609448 |
Filed Date | 2014-06-12 |
United States Patent
Application |
20140159596 |
Kind Code |
A1 |
Sutardja; Sehat ; et
al. |
June 12, 2014 |
PHOSPHOR AND LED PLACEMENT FOR WHITE LED-BASED LAMPS
Abstract
A system including a base portion, which includes first and
second sets of light emitting diodes (LEDs) to emit blue light
having first and second wavelengths in first and second wavelength
ranges in a spectrum of blue light, a glass layer arranged at a
second predetermined distance from the base portion, and a
plurality of coatings of first and second phosphors having a
predetermined length arranged in an alternating pattern on a
surface of the glass layer facing toward the LEDs. The LEDs of the
first and second sets are arranged on the base portion in an
alternating pattern and are separated from each other by a first
predetermined distance. Centers of the coatings of the first and
second phosphors respectively align with centers of corresponding
LEDs in the first and second sets.
Inventors: |
Sutardja; Sehat; (LOS ALTOS
HILLS, CA) ; KRISHNAMOORTHY; RAVISHANKER; (SINGAPORE,
SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MARVELL WORLD TRADE LTD. |
ST. MICHAEL |
|
BB |
|
|
Assignee: |
MARVELL WORLD TRADE LTD.
ST. MICHAEL
BB
|
Family ID: |
48609448 |
Appl. No.: |
14/181088 |
Filed: |
February 14, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13715223 |
Dec 14, 2012 |
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14181088 |
|
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61678513 |
Aug 1, 2012 |
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61576511 |
Dec 16, 2011 |
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Current U.S.
Class: |
315/192 |
Current CPC
Class: |
H05B 45/48 20200101;
F21K 9/64 20160801; H05B 45/24 20200101; H05B 45/35 20200101; H05B
45/10 20200101; H05B 45/46 20200101; H05B 45/20 20200101; H05B
47/10 20200101 |
Class at
Publication: |
315/192 |
International
Class: |
H05B 33/08 20060101
H05B033/08 |
Claims
1. A system comprising: a base portion including (i) a first set of
light emitting diodes configured to emit blue light having first
wavelengths in a first wavelength range in a spectrum of blue
light, and (ii) a second set of light emitting diodes configured to
emit blue light having second wavelengths in a second wavelength
range in the spectrum of blue light, wherein light emitting diodes
of the first set and the second set of light emitting diodes are
(i) arranged on the base portion in an alternating pattern, and
(ii) are separated from each other by a first predetermined
distance; a glass layer arranged at a second predetermined distance
from the base portion; and a plurality of coatings of a first
phosphor and a second phosphor arranged in an alternating pattern
on a surface of the glass layer facing toward the light emitting
diodes, wherein each of the coatings has a predetermined length,
wherein centers of the coatings of the first phosphor align with
centers of corresponding light emitting diodes in the first set of
light emitting diodes, and wherein centers of coatings of the
second phosphor align with centers of corresponding light emitting
diodes in the second set of light emitting diodes.
2. The system of claim 1, wherein: the light emitting diodes of the
first set and the second set of light emitting diodes are arranged
on the base portion along a straight line, and the plurality of
coatings of the first phosphor and the second phosphor is arranged
along a straight line on the surface of the glass layer facing
toward the light emitting diodes.
3. The system of claim 1, wherein the first wavelength range has an
upper limit of 450 nanometers, and wherein the second wavelength
range has a lower limit of 470 nanometers.
4. The system of claim 1, wherein: the first wavelength range is
less than a third wavelength range in the spectrum of blue light,
the second wavelength range is greater than the third wavelength
range in the spectrum of blue light, the first phosphor is a green
phosphor, and the second phosphor is a red phosphor.
5. The system of claim 1, wherein: the first phosphor is configured
to (i) convert a first portion of blue light emitted by the first
set of light emitting diodes to green light, and (ii) allow a
second portion of blue light emitted by the first set of light
emitting diodes to escape unconverted; the second phosphor is
configured to (i) convert a third portion of blue light emitted by
the second set of light emitting diodes to red light, and (ii)
allow a fourth portion of blue light emitted by the second set of
light emitting diodes to escape unconverted; and the green light,
the red light, and the second and fourth portions of the blue light
combine to produce white light.
6. The system of claim 5, further comprising a control module
configured to control currents through one or more of (i) the first
set of light emitting diodes, and (ii) the second set of light
emitting diodes to control one or more of (i) a brightness level
and (ii) a color temperature of the white light.
7. A lamp comprising: the system of claim 5; a switch located on
the lamp, wherein the switch is configured to allow a user to
select a color temperature of the white light; and a current
control module configured to control current through at least one
of (i) the first set of light emitting diodes, and (ii) the second
set of light emitting diodes in accordance with the color
temperature of the white light selected by the user.
8. A lamp comprising: a first set of light emitting diodes and a
second set of light emitting diodes respectively configured to emit
blue light having (i) first wavelengths in a first wavelength range
in a spectrum of blue light and (ii) second wavelengths in a second
wavelength range in the spectrum of blue light, wherein the first
set and the second set of light emitting diodes are evenly spaced
in an alternating pattern on a base portion of the lamp; and a
plurality of coatings of green and red phosphors evenly spaced in
an alternating pattern on a glass surface of the lamp, wherein the
green phosphor is configured to (i) convert a first portion of blue
light having the first wavelengths to green light, and (ii) allow a
second portion of blue light having the first wavelengths to escape
unconverted; the red phosphor is configured to (i) convert a third
portion of blue light having the second wavelengths to red light,
and (ii) allow a fourth portion of blue light having the second
wavelengths to escape unconverted; and the green light, the red
light, and the second and fourth portions of the blue light combine
to produce white light.
9. The lamp of claim 8, wherein: the light emitting diodes of the
first set and the second set of light emitting diodes are arranged
on the base portion along a straight line, and the plurality of
coatings of green and red phosphors is arranged along a straight
line on the glass surface.
10. The lamp of claim 8, wherein the first wavelength has an upper
limit of 450 nanometers, and wherein the second wavelength range
has a lower limit of 470 nanometers.
11. The lamp of claim 8, wherein: the first wavelength range is
less than a third wavelength range in the spectrum of blue light,
and the second wavelength range is greater than the third
wavelength range in the spectrum of blue light.
12. The lamp of claim 8, further comprising a control module
configured to control currents through one or more of (i) the first
set of light emitting diodes, and (ii) the second set of light
emitting diodes to control one or more of (i) a brightness level
and (ii) a color temperature of the white light.
13. The lamp of claim 8, further comprising: a switch located on
the lamp, wherein the switch is configured to allow a user to
select a color temperature of the white light; and a current
control module configured to control current through at least one
of (i) the first set of light emitting diodes, and (ii) the second
set of light emitting diodes in accordance with the color
temperature of the white light selected by the user.
14. A lamp comprising: a first set of light emitting diodes and a
second set of light emitting diodes configured to emit blue light
having first wavelengths in a first wavelength range in a spectrum
of blue light; a third set of light emitting diodes configured to
emit ultraviolet light, wherein the first, second, and third sets
of light emitting diodes are evenly spaced in an alternating
pattern on a base portion of the lamp; and a plurality of coatings
of first, second, and third phosphors evenly spaced in an
alternating pattern on a glass surface of the lamp, wherein the
first phosphor is configured to convert the blue light having the
first wavelengths to a first light having a first color, wherein
the second phosphor is configured to convert the blue light having
the first wavelengths to a second light having a second color,
wherein the third phosphor is configured to convert the ultraviolet
light to blue light, and wherein the first light, the second light,
and the blue light combine to produce white light.
15. The lamp of claim 14, wherein: the first, second, and third
sets of light emitting diodes are arranged on the base portion
along a straight line, and the plurality of coatings of the first,
second, and third phosphors is arranged along a straight line on
the glass surface.
16. The lamp of claim 14, wherein the first wavelength is 450
nanometers, and wherein the ultraviolet light has a wavelength of
less than or equal to 400 nanometers.
17. The lamp of claim 14, wherein: the first phosphor is a green
phosphor, and the first color is green; and the second phosphor is
a red phosphor, and the second color is red.
18. The lamp of claim 14, wherein: the first phosphor is a reddish
yellow phosphor, and the first color is reddish yellow; and the
second phosphor is a yellow phosphor, and the second color is
yellow.
19. The lamp of claim 14, wherein: the first phosphor is a red
phosphor, and the first color is red; and the second phosphor is a
yellow phosphor, and the second color is yellow.
20. The lamp of claim 14, further comprising a control module
configured to control currents through one or more of the first,
second, and third sets of light emitting diodes to control one or
more of (i) a brightness level and (ii) a color temperature of the
white light.
21. The lamp of claim 14, further comprising: a switch located on
the lamp, wherein the switch is configured to allow a user to
select a color temperature of the white light; and a current
control module configured to control current through at least one
of the first, second, and third sets of light emitting diodes in
accordance with the color temperature of the white light selected
by the user.
22. A method comprising: arranging, on a base portion of a lamp,
first and second sets of light emitting diodes in an alternating
pattern; separating the first and second sets of light emitting
diodes from each other by a first predetermined distance; emitting,
from the first set of light emitting diodes, blue light having
first wavelengths in a first wavelength range in a spectrum of blue
light; emitting, from the second set of light emitting diodes, blue
light having second wavelengths in a second wavelength range in the
spectrum of blue light; arranging a glass layer at a second
predetermined distance from the base portion; arranging, on a
surface of the glass layer facing toward the first and second sets
of light emitting diodes, a plurality of coatings of a first
phosphor and a second phosphor in an alternating pattern, wherein
each of the coatings has a predetermined length; aligning centers
of the coatings of the first phosphor with centers of corresponding
light emitting diodes in the first set of light emitting diodes;
and aligning centers of coatings of the second phosphor with
centers of corresponding light emitting diodes in the second set of
light emitting diodes.
23. The method of claim 22, further comprising: arranging the first
and second sets of light emitting diodes on the base portion along
a straight line; and arranging the plurality of coatings of the
first phosphor and the second phosphor along a straight line on the
surface of the glass layer facing toward the first and second sets
of light emitting diodes.
24. The method of claim 22, wherein the first wavelength range has
an upper limit of 450 nanometers, and wherein the second wavelength
range has a lower limit of 470 nanometers.
25. The method of claim 22, wherein: the first wavelength range is
less than a third wavelength range in the spectrum of blue light,
the second wavelength range is greater than the third wavelength
range in the spectrum of blue light, the first phosphor is a green
phosphor, and the second phosphor is a red phosphor.
26. The method of claim 22, further comprising: converting, using
the first phosphor, a first portion of blue light emitted by the
first set of light emitting diodes to green light; allowing a
second portion of blue light emitted by the first set of light
emitting diodes to escape unconverted; converting, using the second
phosphor, a third portion of blue light emitted by the second set
of light emitting diodes to red light; allowing a fourth portion of
blue light emitted by the second set of light emitting diodes to
escape unconverted; and producing white light by combining the
green light, the red light, and the second and fourth portions of
the blue light.
27. The method of claim 26, further comprising controlling currents
through one or more of (i) the first set of light emitting diodes,
and (ii) the second set of light emitting diodes to control one or
more of (i) a brightness level and (ii) a color temperature of the
white light.
28. The method of claim 26, further comprising: selecting a color
temperature of the white light using a switch located on the lamp;
and controlling current through at least one of (i) the first set
of light emitting diodes, and (ii) the second set of light emitting
diodes in accordance with the color temperature of the white light
selected by a user.
29. A method comprising: arranging, on a base portion of a lamp,
first, second, and third sets of light emitting diodes in an
alternating pattern, wherein the first, second, and third sets of
light emitting diodes are evenly spaced on the base portion of the
lamp; emitting, from first and second sets of light emitting
diodes, blue light having first wavelengths in a first wavelength
range in a spectrum of blue light; emitting ultraviolet light from
a third set of light emitting diodes; arranging, a plurality of
coatings of first, second, and third phosphors in an alternating
pattern on a glass surface of the lamp, wherein the first, second,
and third phosphors are evenly spaced; converting, using the first
phosphor, the blue light having the first wavelengths to a first
light having a first color; converting, using the second phosphor,
the blue light having the first wavelengths to a second light
having a second color; converting, using the third phosphor, the
ultraviolet light to blue light; and producing white light by
combining the first light, the second light, and the blue
light.
30. The method of claim 29, further comprising: arranging the
first, second, and third sets of light emitting diodes on the base
portion along a straight line; and arranging the plurality of
coatings of the first, second, and third phosphors along a straight
line on the glass surface.
31. The method of claim 29, wherein the first wavelength is 450
nanometers, and wherein the ultraviolet light has a wavelength of
less than or equal to 400 nanometers.
32. The method of claim 29, wherein: the first phosphor is a green
phosphor, and the first color is green; and the second phosphor is
a red phosphor, and the second color is red.
33. The method of claim 29, wherein: the first phosphor is a
reddish yellow phosphor, and the first color is reddish yellow; and
the second phosphor is a yellow phosphor, and the second color is
yellow.
34. The method of claim 29, wherein: the first phosphor is a red
phosphor, and the first color is red; and the second phosphor is a
yellow phosphor, and the second color is yellow.
35. The method of claim 29, further comprising controlling currents
through one or more of the first, second, and third sets of light
emitting diodes to control one or more of (i) a brightness level
and (ii) a color temperature of the white light.
36. The method of claim 29, further comprising: selecting a color
temperature of the white light using a switch located on the lamp;
and controlling current through at least one of the first, second,
and third sets of light emitting diodes in accordance with the
color temperature of the white light selected by a user.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present disclosure is a divisional of U.S. patent
application Ser. No. 13/715,223 filed on Dec. 14, 2012, which
claims the benefit of U.S. Provisional Application No. 61/678,513,
filed Aug. 1, 2012 and U.S. Provisional Application No. 61/576,511,
filed Dec. 16, 2011. The entire disclosures of the above
applications are incorporated herein by reference.
FIELD
[0002] The present disclosure relates generally to light emitting
diode (LED)-based illumination systems and more particularly to
LED-based tube lights and lamps for illuminating large areas.
BACKGROUND
[0003] The background description provided herein is for the
purpose of generally presenting the context of the disclosure. Work
of the presently named inventors, to the extent the work is
described in this background section, as well as aspects of the
description that may not otherwise qualify as prior art at the time
of filing, are neither expressly nor impliedly admitted as prior
art against the present disclosure.
[0004] Light emitting diode (LED)-based illumination systems are
being increasingly used particularly in commercial applications.
Some examples of commercial applications where LED-based
illumination systems are used include billboards, computer
displays, and television screens. LED-based lamps can also be used
in home and office environments. For example, LED-based lamps
having the shape of a conventional light bulb or a tube light can
be used in home and office environments. LED-based lamps that can
be used in home and office environments, however, are not yet as
affordable as incandescent and fluorescent lamps.
[0005] Lamps that generate white light are generally preferred in
home and office environments. LEDs can be used to manufacture lamps
that generate white light. For example, LEDs that generate red,
green, and blue light can be used to manufacture lamps that
generate white light. Specifically, light generated by red, green,
and blue LEDs can be combined to produce white light. LEDs that
generate pure red and green light, however, can be relatively
expensive.
[0006] Alternatively, LEDs that generate blue light and phosphors
that convert blue light into red and green light can be used to
produce white light. Specifically, blue LEDs can be coated with a
mixture of red and green phosphors. Some of the blue light output
by the blue LEDs is converted to red and green light by the red and
green phosphors, respectively. Some of the blue light output by the
blue LEDs may escape the phosphors without getting converted. The
red and green light converted by the phosphors combines with the
blue light that escapes unconverted to produce white light.
[0007] The mixture of red and green phosphors produces optimum
light output when excited by blue light having specific
wavelengths. For example, most red and green phosphors convert blue
light optimally when the wavelength of the blue light is
approximately 450 nm. Accordingly, blue LEDs that produce blue
light within a narrow range of wavelengths (e.g., 450 nm.+-.5 nm)
are typically selected to generate white light, and blue LEDs that
produce light having wavelengths outside of the narrow range of
wavelengths are typically rejected. The stringent selection process
and rejection of numerous LEDs increases the cost of generating
white light using blue LEDs. Additionally, the coating of the
phosphor mixture may not be uniform across the LEDs. Due to
variations in the coating, the whiteness of the light produced by
the LEDs may vary from LED to LED. Accordingly, the LEDs need to be
selected using a binning process, which further increases cost.
SUMMARY
[0008] A system includes a first transistor, a second transistor,
and a comparator. The first transistor is configured to supply a
first current to a first load connected to a first terminal of the
first transistor. The second transistor is configured to supply a
second current to a second load connected to a first terminal of
the second transistor, where the first current and the second
current have a predetermined ratio. The comparator is configured to
compare a voltage at the first terminal of the first transistor or
a voltage at the first terminal of the second transistor to a
reference voltage, and to adjust, based on the comparison, biasing
of the first transistor and the second transistor to maintain the
predetermined ratio between the first current and the second
current.
[0009] In other features, in response to a change in the first
current, the adjusted biasing changes the second current in
accordance with the predetermined ratio between the first current
and the second current.
[0010] In other features, the predetermined ratio between the first
current and the second current is based on a ratio of areas of the
first transistor and the second transistor.
[0011] In other features, in response to a change in power received
by the first load and the second load, the comparator is configured
to adjust the biasing of the first transistor and the second
transistor to maintain the predetermined ratio between the first
current and the second current.
[0012] In other features, in response to a change in power received
by the first load and the second load, the comparator is configured
to adjust the first current and the second current to maintain the
predetermined ratio between the first current and the second
current.
[0013] In other features, the first load includes a first set of
light emitting diodes configured to generate light having first
wavelengths in a first wavelength range in a spectrum of blue
light. The second load includes a second set of light emitting
diodes configured to generate light having second wavelengths in a
second wavelength range in the spectrum of blue light. The first
wavelength range is less than a third wavelength range in the
spectrum of blue light. The second wavelength range is greater than
the third wavelength range. The light generated by the first set of
light emitting diodes and the second set of light emitting diodes
combines to produce white light. A color temperature of the white
light depends on the predetermined ratio.
[0014] In other features, the first wavelengths are less than or
equal to 450 nanometers, and the second wavelengths are greater
than or equal to 470 nanometers.
[0015] In other features, the first wavelengths are between 420
nanometers and 450 nanometers, and the second wavelengths are
between 470 nanometers and 490 nanometers.
[0016] In other features, the first load includes a first set of
light emitting diodes configured to generate blue light having
first wavelengths in a first wavelength range in a spectrum of blue
light. The second load includes a second set of light emitting
diodes configured to generate blue light having second wavelengths
in a second wavelength range in the spectrum of blue light. The
system further comprises a green phosphor configured to convert a
first portion of the blue light having the first wavelengths into
green light, and allow a second portion of the blue light having
the first wavelengths to escape unconverted. The system further
comprises a red phosphor configured to convert a third portion of
the blue light having the second wavelengths into red light, and
allow a fourth portion of the blue light having the second
wavelengths to escape unconverted. The green light, the red light,
the second portion of the blue light having the first wavelengths,
and fourth portion of the blue light having the second wavelengths
combine to produce white light. A color temperature of the white
light depends on the predetermined ratio.
[0017] In other features, the first wavelength range is less than a
third wavelength range in the spectrum of blue light, and the
second wavelength range is greater than the third wavelength
range.
[0018] In still other features, a system includes a first
transistor, a second transistor, a third transistor, and a
comparator. The first transistor is configured to supply a first
current to a first set of light emitting diodes connected to a
first terminal of the first transistor. The first set of light
emitting diodes is configured to output light having first
wavelengths in a first wavelength range in a spectrum of blue
light. The second transistor is configured to supply a second
current to a second set of light emitting diodes connected to a
first terminal of the second transistor. The second set of light
emitting diodes is configured to output light having second
wavelengths in a second wavelength range in the spectrum of blue
light. The third transistor is configured to supply a third current
to a third set of light emitting diodes connected to a first
terminal of the third transistor. The third set of light emitting
diodes is configured to output light having third wavelengths in a
third wavelength range in the spectrum of blue light. The third
wavelength range is (i) less than the second wavelength range and
(ii) greater than the first wavelength range. Values of the first
current, the second current, and the third current are in a
predetermined proportion. The light having the first, second, and
third wavelengths combines to generate white light. The comparator
is configured to compare a voltage at the first terminal of the
first transistor, a voltage at the first terminal of the second
transistor, or a voltage at the first terminal of the third
transistor to a reference voltage, and to adjust, based on the
comparison, biasing of the first transistor, the second transistor,
and the third transistor to maintain the predetermined proportion
between the first current, the second current, and the third
current. A color temperature of the white light depends on the
predetermined proportion of the first current, the second current,
and the third current.
[0019] In still other features, a method comprises supplying a
first current to a first load connected to a first terminal of a
first transistor. The method further comprises supplying a second
current to a second load connected to a first terminal of a second
transistor, where the first current and the second current have a
predetermined ratio. The method further comprises comparing a
voltage at the first terminal of the first transistor or a voltage
at the first terminal of the second transistor to a reference
voltage. The method further comprises adjusting, based on the
comparison, biasing of the first transistor and the second
transistor to maintain the predetermined ratio between the first
current and the second current.
[0020] In still other features, a method comprises supplying a
first current to a first set of light emitting diodes connected to
a first terminal of a first transistor. The method further
comprises outputting, from the first set of light emitting diodes,
light having first wavelengths in a first wavelength range in a
spectrum of blue light. The method further comprises supplying a
second current to a second set of light emitting diodes connected
to a first terminal of a second transistor. The method further
comprises outputting, from the second set of light emitting diodes,
light having the first wavelengths in the first wavelength range in
the spectrum of blue light. The method further comprises supplying
a third current to a third set of light emitting diodes connected
to a first terminal of a third transistor. The method further
comprises outputting, from the third set of light emitting diodes,
light having second wavelengths in a second wavelength range in a
spectrum of ultraviolet light, where values of the first current,
the second current, and the third current are in a predetermined
proportion. The method further comprises comparing a voltage at the
first terminal of the first transistor, a voltage at the first
terminal of the second transistor, or a voltage at the first
terminal of the third transistor to a reference voltage. The method
further comprises adjusting, based on the comparison, biasing of
the first transistor, the second transistor, and the third
transistor to maintain the predetermined proportion between the
first current, the second current, and the third current. A color
temperature of white light generated based on the light output by
the first, second, and third sets of light emitting diodes depends
on the predetermined proportion of the first current, the second
current, and the third current.
[0021] In still other features, a system includes a first set of
light emitting diodes, a second set of light emitting diodes, and a
control module. The first set of light emitting diodes is
configured to emit blue light having first wavelengths in a first
wavelength range in a spectrum of blue light. The first set of
light emitting diodes includes a green phosphor configured to
convert the blue light having the first wavelengths to green light.
The second set of light emitting diodes is configured to emit blue
light having second wavelengths in a second wavelength range in the
spectrum of blue light. The second set of light emitting diodes
includes a red phosphor configured to convert the blue light having
the second wavelengths to red light. The first wavelength range is
less than the second wavelength range. The control module is
configured to control currents through the first set of light
emitting diodes and the second set of light emitting diodes.
[0022] In other features, the system further comprises a third set
of light emitting diodes configured to emit blue light having third
wavelengths in a third wavelength range in the spectrum of blue
light. The third wavelength range is (i) less than the second
wavelength range and (ii) greater than the first wavelength range.
The control module is configured to control current through the
third set of light emitting diodes.
[0023] In other features, the system further comprises a third set
of light emitting diodes configured to emit blue light having a
plurality of wavelengths in a third wavelength range in the
spectrum of blue light. The third wavelength range is (i) less than
the second wavelength range and (ii) greater than the first
wavelength range. Light emitting diodes in the third set of light
emitting diodes are arranged in a predetermined order. The
predetermined order is based on the plurality of wavelengths. The
control module is configured to control current through the third
set of light emitting diodes.
[0024] In other features, the system further comprises a third set
of light emitting diodes that (i) is configured to emit ultraviolet
light and (ii) includes a phosphor configured to convert the
ultraviolet light into blue light having third wavelengths in a
third wavelength range in the spectrum of blue light. The third
wavelength range is (i) less than the second wavelength range and
(ii) greater than the first wavelength range. The control module is
configured to control current through the third set of light
emitting diodes.
[0025] In other features, the green light generated from the first
set of light emitting diodes, the red light generated from the
second set of light emitting diodes, and the blue light generated
from the third set of light emitting diodes combine to generate
white light. The control module is configured to control currents
through the first set of light emitting diodes, the second set of
light emitting diodes, and the third set of light emitting diodes
to control at least one of (i) brightness and (ii) a color
temperature of the white light.
[0026] In other features, the system further comprises a third set
of light emitting diodes configured to emit blue light having third
wavelengths in a third wavelength range in the spectrum of blue
light. The third wavelength range is (i) less than the second
wavelength range and (ii) greater than the first wavelength range.
The third set of light emitting diodes includes an amber phosphor
configured to (i) convert a portion of the blue light having the
third wavelengths to red light and (ii) allow a remainder of the
blue light having the third wavelengths to pass through the amber
phosphor unconverted. The control module is configured to control
current through the third set of light emitting diodes and decrease
current through the second set of light emitting diodes based on an
amount of red light output by the third set of light emitting
diodes.
[0027] In still other features, a system includes a first set of
light emitting diodes, a second set of light emitting diodes, and a
control module. The first set of light emitting diodes is
configured to emit blue light having first wavelengths in a first
wavelength range. The first wavelength range corresponds to a first
of three portions of a spectrum of blue light. The three portions
of the spectrum of blue light include wavelengths of blue light in
ascending order. The first portion includes wavelengths shorter
than the second and third of the three portions. The first set of
light emitting diodes includes a first phosphor configured to
convert the blue light having the first wavelengths to green light.
The second set of light emitting diodes is configured to emit blue
light having second wavelengths in a second wavelength range. The
second wavelength range corresponds to the third portion of the
spectrum of blue light. The third portion includes wavelengths
longer than the first and second portions. The second set of light
emitting diodes includes a second phosphor configured to convert
the blue light having the second wavelengths to red light. The
control module is configured to control currents through the first
set of light emitting diodes and the second set of light emitting
diodes.
[0028] In other features, the system further comprises a third set
of light emitting diodes configured to emit blue light having third
wavelengths in a third wavelength range. The third wavelength range
corresponds to the second portion of the spectrum of blue light.
The second portion includes wavelengths longer than the first
portion and shorter than the third portion. The control module is
configured to control current through the third set of light
emitting diodes.
[0029] In other features, the system further comprises a third set
of light emitting diodes configured to emit blue light having a
plurality of wavelengths in a third wavelength range. The third
wavelength range corresponds to the second portion of the spectrum
of blue light. The second portion includes wavelengths longer than
the first portion and shorter than the third portion. Light
emitting diodes in the third set of light emitting diodes are
arranged in a predetermined order. The predetermined order is based
on the plurality of wavelengths. The control module is configured
to control current through the third set of light emitting
diodes.
[0030] In other features, the system further comprises a third set
of light emitting diodes that (i) is configured to emit ultraviolet
light and (ii) includes a phosphor configured to convert the
ultraviolet light into blue light having third wavelengths in a
third wavelength range. The third wavelength range corresponds to
the second portion of the spectrum of blue light. The second
portion includes wavelengths longer than the first portion and
shorter than the third portion. The control module is configured to
control current through the third set of light emitting diodes.
[0031] In other features, the system further comprises a third set
of light emitting diodes configured to emit blue light having third
wavelengths in a third wavelength range. The third wavelength range
corresponds to the second portion of the spectrum of blue light.
The second portion includes wavelengths longer than the first
portion and shorter than the third portion. The third set of light
emitting diodes includes a third phosphor configured to (i) convert
a portion of the blue light having the third wavelengths to red
light and (ii) allow a remainder of the blue light emitted by the
third set of light emitting diodes to pass through the third
phosphor unconverted. The control module is configured to control
current through the third set of light emitting diodes and decrease
current through the second set of light emitting diodes based on an
amount of red light generated from the third set of light emitting
diodes.
[0032] In still other features, a system includes first, second,
and third sets of light emitting diodes and a control module. The
first set of light emitting diodes is configured to emit blue light
having first wavelengths in a first wavelength range in a spectrum
of blue light. The first set of light emitting diodes includes a
first phosphor configured to convert the blue light having the
first wavelengths to light of a first color. The second set of
light emitting diodes is configured to emit blue light having the
first wavelengths in the first wavelength range in the spectrum of
blue light. The second set of light emitting diodes includes a
second phosphor configured to convert the blue light having the
first wavelengths to light of a second color. The third set of
emitting diodes is configured to emit ultraviolet light having
second wavelengths in a second wavelength range in a spectrum of
ultraviolet light. The third set of light emitting diodes includes
a third phosphor configured to convert the ultraviolet light having
the second wavelengths to blue light. The control module is
configured to control currents through the first, second, and third
sets of light emitting diodes. The light having first and second
colors combines with the blue light generated by the third set of
light emitting diodes to produce white light. A color temperature
of the white light is based on the currents through the first,
second, and third sets of light emitting diodes.
[0033] In other features, the first phosphor is a green phosphor,
and the first color is green; the second phosphor is a red
phosphor, and the second color is red; and the light having green
and red colors combines with the blue light to produce the white
light.
[0034] In other features, the first phosphor is a reddish yellow
phosphor, and the first color is reddish yellow; the second
phosphor is a yellow phosphor, and the second color is yellow; and
the light having reddish yellow and yellow colors combines with the
blue light to produce the white light.
[0035] In other features, the first phosphor is a red phosphor, and
the first color is red; the second phosphor is a yellow phosphor,
and the second color is yellow; and the light having red and yellow
colors combines with the blue light to produce the white light.
[0036] In still other features, a method comprises emitting, from a
first set of light emitting diodes, blue light having first
wavelengths in a first wavelength range in a spectrum of blue
light. The method further comprises converting, using a green
phosphor, the blue light having the first wavelengths to green
light. The method further comprises emitting, from a second set of
light emitting diodes, blue light having second wavelengths in a
second wavelength range in the spectrum of blue light, where the
first wavelength range is less than the second wavelength range.
The method further comprises converting, using a red phosphor, the
blue light having the second wavelengths to red light. The method
further comprises controlling currents through the first set of
light emitting diodes and the second set of light emitting
diodes.
[0037] In other features, the method further comprises emitting,
from a third set of light emitting diodes, blue light having third
wavelengths in a third wavelength range in the spectrum of blue
light, where the third wavelength range is (i) less than the second
wavelength range and (ii) greater than the first wavelength range;
and controlling current through the third set of light emitting
diodes.
[0038] In other features, the method further comprises arranging a
third set of light emitting diodes in a predetermined order, where
the predetermined order is based on a plurality of wavelengths. The
method further comprises emitting, from the third set of light
emitting diodes, blue light having the plurality of wavelengths in
a third wavelength range in the spectrum of blue light, where the
third wavelength range is (i) less than the second wavelength range
and (ii) greater than the first wavelength range. The method
further comprises controlling current through the third set of
light emitting diodes.
[0039] In other features, the method further comprises emitting,
from a third set of light emitting diodes, ultraviolet light. The
method further comprises converting, using a phosphor, the
ultraviolet light into blue light having third wavelengths in a
third wavelength range in the spectrum of blue light, where the
third wavelength range is (i) less than the second wavelength range
and (ii) greater than the first wavelength range. The method
further comprises controlling current through the third set of
light emitting diodes.
[0040] In other features, the method further comprises emitting,
from a third set of light emitting diodes, blue light having third
wavelengths in a third wavelength range in the spectrum of blue
light, where the third wavelength range is (i) less than the second
wavelength range and (ii) greater than the first wavelength range.
The method further comprises converting, using an amber phosphor, a
portion of the blue light having the third wavelengths to red
light. The method further comprises allowing a remainder of the
blue light having the third wavelengths to pass through the amber
phosphor unconverted. The method further comprises controlling
current through the third set of light emitting diodes and decrease
current through the second set of light emitting diodes based on an
amount of red light generated from the third set of light emitting
diodes.
[0041] In still other features, a method comprises emitting, using
a first set of light emitting diodes, blue light having first
wavelengths in a first wavelength range in a spectrum of blue
light. The method further comprises converting, using a first
phosphor, the blue light having the first wavelengths to light of a
first color. The method further comprises emitting, using a second
set of light emitting diodes, blue light having the first
wavelengths in the first wavelength range in the spectrum of blue
light. The method further comprises converting, using a second
phosphor, the blue light having the first wavelengths to light of a
second color. The method further comprises emitting, using a third
set of emitting diodes, ultraviolet light having second wavelengths
in a second wavelength range in a spectrum of ultraviolet light.
The method further comprises converting, using a third phosphor,
the ultraviolet light having the second wavelengths to blue light.
The method further comprises controlling currents through the
first, second, and third sets of light emitting diodes. The method
further comprises producing white light by combining the light
having first and second colors with the blue light generated by the
third set of light emitting diodes. The method further comprises
controlling a color temperature of the white light is based on the
currents through the first, second, and third sets of light
emitting diodes.
[0042] In still other features, a lamp includes a first set of
light emitting diodes configured to generate first light, a second
set of light emitting diodes configured to generate second light,
and a third set of light emitting diodes configured to generate
third light. The first light, the second light, and the third light
combine to produce white light. A first switch is located at a base
portion of the lamp. A state of the first switch corresponds to a
color temperature of the white light. A color temperature
adjustment module is configured to vary outputs of the first,
second, and third sets of light emitting diodes in accordance with
the color temperature of the white light selected by a user using
the first switch.
[0043] In other features, the color temperature adjustment module
includes a current control module configured to control current
through at least one of (i) the first set of light emitting diodes,
(ii) the second set of light emitting diodes, and (iii) the third
set of light emitting diodes in accordance with the color
temperature of the white light selected by the user using the first
switch.
[0044] In other features, the first switch is configured to allow
the user to select the color temperature of the white light from a
group consisting of 4000 degrees Kelvin, 3500 degrees Kelvin, 3000
degrees Kelvin, 2700 degrees Kelvin.
[0045] In other features, the lamp further comprises a current
control module configured to supply a first current to the first
set of light emitting diodes, supply a second current to the second
set of light emitting diodes, supply a third current to the third
set of light emitting diodes, select a first proportion for the
first current, the second current, and the third current in
response to the user setting the first switch to a first position,
and select a second proportion for the first current, the second
current, and the third current in response to the user setting the
first switch to a second position.
[0046] In still other features, a lamp includes first, second, and
third sets of light emitting diodes, a first switch, and a color
temperature adjustment module. The first set of light emitting
diodes is configured to emit blue light having first wavelengths in
a first wavelength range in a spectrum of blue light. The first set
of light emitting diodes includes a first phosphor configured to
convert the blue light having the first wavelengths to light of a
first color. The second set of light emitting diodes is configured
to emit blue light having the first wavelengths in the first
wavelength range in the spectrum of blue light. The second set of
light emitting diodes includes a second phosphor configured to
convert the blue light having the first wavelengths to light of a
second color. The third set of light emitting diodes is configured
to emit ultraviolet light having second wavelengths in a second
wavelength range in a spectrum of ultraviolet light. The third set
of light emitting diodes includes a third phosphor configured to
convert the ultraviolet light having the second wavelengths to blue
light. The light having the first and second colors combines with
the blue light generated by the third set of light emitting diodes
to produce white light. The first switch is located at a base
portion of the lamp. A state of the first switch corresponds to a
color temperature of the white light. The color temperature
adjustment module is configured to vary outputs of the first,
second, and third sets of light emitting diodes in accordance with
the color temperature of the white light selected by a user using
the first switch.
[0047] In still other features, a method comprises generating first
light using a first set of light emitting diodes, generating second
light using a second set of light emitting diodes, and generating
third light using a third set of light emitting diodes. The method
further comprises producing white light by combining the first
light, the second light, and the third light. The method further
comprises changing a state of a first switch located at a base
portion of a lamp comprising the first, second, and third sets of
light emitting diodes, where the state of the first switch
corresponds to a color temperature of the white light. The method
further comprises varying outputs of the first, second, and third
sets of light emitting diodes in accordance with the color
temperature of the white light selected by a user using the first
switch.
[0048] In still other features, a method comprises emitting, using
a first set of light emitting diodes, blue light having first
wavelengths in a first wavelength range in a spectrum of blue
light. The method further comprises converting, using a first
phosphor, the blue light having the first wavelengths to light of a
first color. The method further comprises emitting, using a second
set of light emitting diodes, blue light having the first
wavelengths in the first wavelength range in the spectrum of blue
light. The method further comprises converting, using a second
phosphor, the blue light having the first wavelengths to light of a
second color. The method further comprises emitting, using a third
set of light emitting diodes, ultraviolet light having second
wavelengths in a second wavelength range in a spectrum of
ultraviolet light. The method further comprises converting, using a
third phosphor, the ultraviolet light having the second wavelengths
to blue light. The method further comprises producing white light
by combining the light having the first and second colors with the
blue light generated by the third set of light emitting diodes. The
method further comprises changing a state of a first switch located
at a base portion of a lamp comprising the first, second, and third
sets of light emitting diodes, where the state of the first switch
corresponds to a color temperature of the white light. The method
further comprises varying outputs of the first, second, and third
sets of light emitting diodes in accordance with the color
temperature of the white light selected by a user using the first
switch.
[0049] In still other features, a system includes a base portion, a
glass layer, and a plurality of coatings of a first phosphor and a
second phosphor. The base portion includes (i) a first set of light
emitting diodes configured to emit blue light having first
wavelengths in a first wavelength range in a spectrum of blue
light, and (ii) a second set of light emitting diodes configured to
emit blue light having second wavelengths in a second wavelength
range in the spectrum of blue light. Light emitting diodes of the
first set and the second set of light emitting diodes are (i)
arranged on the base portion in an alternating pattern, and (ii)
are separated from each other by a first predetermined distance.
The glass layer is arranged at a second predetermined distance from
the base portion. The plurality of coatings of a first phosphor and
a second phosphor is arranged in an alternating pattern on a
surface of the glass layer facing toward the light emitting diodes.
Each of the coatings has a predetermined length. Centers of the
coatings of the first phosphor align with centers of corresponding
light emitting diodes in the first set of light emitting diodes.
Centers of coatings of the second phosphor align with centers of
corresponding light emitting diodes in the second set of light
emitting diodes.
[0050] In other features, the light emitting diodes of the first
set and the second set of light emitting diodes are arranged on the
base portion along a straight line, and the plurality of coatings
of the first phosphor and the second phosphor is arranged along a
straight line on the surface of the glass layer facing toward the
light emitting diodes.
[0051] In still other features, a lamp includes a first set of
light emitting diodes and a second set of light emitting diodes,
and a plurality of coatings of green and red phosphors. The first
set of light emitting diodes and a second set of light emitting
diodes are respectively configured to emit blue light having (i)
first wavelengths in a first wavelength range in a spectrum of blue
light and (ii) second wavelengths in a second wavelength range in
the spectrum of blue light. The first set and the second set of
light emitting diodes are evenly spaced in an alternating pattern
on a base portion of the lamp. The plurality of coatings of green
and red phosphors is evenly spaced in an alternating pattern on a
glass surface of the lamp. The green phosphor is configured to
convert a first portion of blue light having the first wavelengths
to green light and to allow a second portion of blue light having
the first wavelengths to escape unconverted. The red phosphor is
configured to convert a third portion of blue light having the
second wavelengths to red light, and to allow a fourth portion of
blue light having the second wavelengths to escape unconverted. The
green light, the red light, and the second and fourth portions of
the blue light combine to produce white light.
[0052] In still other features, a lamp includes first, second, and
third sets of light emitting diodes, and a plurality of coatings of
first, second, and third phosphors. The first set of light emitting
diodes and the second set of light emitting diodes are configured
to emit blue light having first wavelengths in a first wavelength
range in a spectrum of blue light. The third set of light emitting
diodes is configured to emit ultraviolet light. The first, second,
and third sets of light emitting diodes are evenly spaced in an
alternating pattern on a base portion of the lamp. The plurality of
coatings of first, second, and third phosphors is evenly spaced in
an alternating pattern on a glass surface of the lamp. The first
phosphor is configured to convert the blue light having the first
wavelengths to a first light having a first color. The second
phosphor is configured to convert the blue light having the first
wavelengths to a second light having a second color. The third
phosphor is configured to convert the ultraviolet light to blue
light. The first light, the second light, and the blue light
combine to produce white light.
[0053] In still other features, a method comprises arranging, on a
base portion of a lamp, first and second sets of light emitting
diodes in an alternating pattern; and separating the first and
second sets of light emitting diodes from each other by a first
predetermined distance. The method further comprises emitting, from
the first set of light emitting diodes, blue light having first
wavelengths in a first wavelength range in a spectrum of blue
light. The method further comprises emitting, from the second set
of light emitting diodes, blue light having second wavelengths in a
second wavelength range in the spectrum of blue light. The method
further comprises arranging a glass layer at a second predetermined
distance from the base portion; and arranging, on a surface of the
glass layer facing toward the first and second sets of light
emitting diodes, a plurality of coatings of a first phosphor and a
second phosphor in an alternating pattern, where each of the
coatings has a predetermined length. The method further comprises
aligning centers of the coatings of the first phosphor with centers
of corresponding light emitting diodes in the first set of light
emitting diodes; and aligning centers of coatings of the second
phosphor with centers of corresponding light emitting diodes in the
second set of light emitting diodes.
[0054] In still other features, a method comprises arranging, on a
base portion of a lamp, first, second, and third sets of light
emitting diodes in an alternating pattern, where the first, second,
and third sets of light emitting diodes are evenly spaced on the
base portion of the lamp. The method further comprises emitting,
from first and second sets of light emitting diodes, blue light
having first wavelengths in a first wavelength range in a spectrum
of blue light. The method further comprises emitting ultraviolet
light from a third set of light emitting diodes. The method further
comprises arranging, a plurality of coatings of first, second, and
third phosphors in an alternating pattern on a glass surface of the
lamp, where the first, second, and third phosphors are evenly
spaced. The method further comprises converting, using the first
phosphor, the blue light having the first wavelengths to a first
light having a first color. The method further comprises
converting, using the second phosphor, the blue light having the
first wavelengths to a second light having a second color. The
method further comprises converting, using the third phosphor, the
ultraviolet light to blue light. The method further comprises
producing white light by combining the first light, the second
light, and the blue light.
[0055] Further areas of applicability of the present disclosure
will become apparent from the detailed description, the claims and
the drawings. The detailed description and specific examples are
intended for purposes of illustration only and are not intended to
limit the scope of the disclosure.
BRIEF DESCRIPTION OF DRAWINGS
[0056] The present disclosure will become more fully understood
from the detailed description and the accompanying drawings,
wherein:
[0057] FIG. 1 is a functional block diagram of a light emitting
diode (LED)-based lamp according to the present disclosure;
[0058] FIG. 2 is a detailed functional block diagram of the
LED-based lamp of FIG. 1 according to the present disclosure;
[0059] FIG. 3A depicts a LED lamp having the shape of a
conventional light bulb that uses LEDs according to the present
disclosure;
[0060] FIG. 3B is a functional block diagram of the LED lamp of
FIG. 3A;
[0061] FIG. 4 depicts a current control module to control currents
through a plurality of strings of LEDs according to the present
disclosure;
[0062] FIG. 5A depicts a LED lamp having the shape of a
conventional tube light that uses LED and phosphor layouts
according to the present disclosure;
[0063] FIG. 5B depicts the LED and phosphor layouts of the LED lamp
of FIG. 5A;
[0064] FIG. 6 depicts a current control module to control currents
through a plurality of strings of LEDs used in the LED lamp of FIG.
5A according to the present disclosure;
[0065] FIG. 7 is a schematic of a current balancing circuit that
uses current mirroring and feedback to control currents through a
plurality of loads according to the present disclosure;
[0066] FIG. 8 is a schematic of a simple current mirror circuit
that controls currents through a plurality of LED strings used in
one or more LED lamps disclosed herein;
[0067] FIG. 9 is a schematic of a current balancing circuit that
uses current mirroring and feedback to control currents through a
plurality of LED strings used in one or more LED lamps according to
the present disclosure; and
[0068] FIG. 10 is a flowchart of a method for controlling current
through a plurality of LED strings in one or more LED lamps
according to the present disclosure;
[0069] FIGS. 11A-11C depicts additional ways of generating white
light using blue LEDs, ultraviolet LEDs, and phosphors according to
the present disclosure;
[0070] FIG. 11D depicts LED and phosphor layouts of an LED lamp
having the shape of a conventional tube light that uses one of the
additional ways of generating white light shown in FIGS.
11A-11C;
[0071] FIG. 12A depicts one of a plurality of LED strings used to
produce blue light used in producing white light, where the LED
string includes LEDs producing ultraviolet light that is converted
to blue light by a blue phosphor;
[0072] FIG. 12B depicts of a plurality of LED strings used to
produce blue light used in producing white light, where the LED
string includes blue LEDs generating blue light having preselected
wavelengths, and where the blue LEDs are arranged in a
predetermined order;
[0073] FIG. 13 is a flowchart of a method for generating white
light according to the present disclosure; and
[0074] FIG. 14 is a flow chart of a method for controlling currents
through a plurality of strings of LEDs used in the LED lamps
disclosed herein according to the present disclosure.
DESCRIPTION
[0075] Blue LEDs that output light over a wide range of wavelengths
can be used to generate white light. Specifically, blue LEDs that
output light having wavelengths closer to a lower end of a spectrum
of blue light (e.g., less than 450 nm) and an upper end of the
spectrum of blue light (e.g., greater than 470 nm) can be utilized.
Additionally, blue LEDs that output light having wavelengths within
a range around 450 nm can also be used. Thus, essentially, blue
LEDs that output light having wavelengths spanning an entire
spectrum of blue light can be utilized to generate white light.
[0076] More specifically, a first set of blue LEDs that output blue
light having first wavelengths closer to the lower end of the
spectrum of blue light (e.g., less than 450 nm) can be used to
generate green light. A second set of blue LEDs that output blue
light having second wavelengths closer to the upper end of the
spectrum of blue light (e.g., greater than 470 nm) can be used to
generate red light. Additionally, a third set of blue LEDs that
output light having wavelengths between the first and second
wavelengths can also be used. For example only, the third set of
LEDs may produce blue light having wavelengths within a range of
about .+-.5 nm, .+-.10 nm, or .+-.15 nm around 450 nm.
Alternatively, the third set of LEDs may include LEDs that emit
ultraviolet light instead of blue light and may be coated with a
phosphor that converts the ultraviolet light into a wideband blue
light. The wideband blue light may have wavelengths spanning an
entire spectrum of blue light including wavelengths less than or
equal to 450 nm, 450 nm-470 nm, and wavelengths greater than or
equal to 470 nm.
[0077] The first set of LEDs can be coated with a green phosphor
that converts the blue light having the first wavelengths to green
light. The second set of LEDs can be coated with a red phosphor
that converts the blue light having the second wavelengths to red
light. The third set of LEDs may not be coated with a phosphor that
converts blue light into a light of a different color. The green,
red, and blue light output by the first, second, and third sets of
LEDs can be combined to produce white light. Accordingly, the first
and second sets of LEDs that would otherwise be rejected can be
utilized to generate white light. Utilizing LEDs that are typically
rejected can reduce the cost of LED-based lamps generating white
light.
[0078] Since white light can be produced using less blue light and
more red light, the third set of LEDs producing blue light may be
coated with amber phosphor. The amber phosphor can be coated so
that only a portion of the blue light produced by the third set of
LEDs is converted to red light, and some of the blue light produced
by the third set of LEDs can escape unconverted through the amber
phosphor. Since the third set of LEDs and the amber phosphor would
produce some of the red light required to generate white light,
current through the second set of LEDs that produce red light may
be reduced to produce less red light. White light is produced by a
sum of the red light produced by the second and third sets of LEDs,
green light produced by the first set of LEDs, and blue light that
escapes unconverted from the second and third sets of LEDs.
[0079] Brightness and/or color temperature (also called whiteness)
of the white light can be controlled by controlling current through
one or more sets of the LEDs individually. For example, if white
light is produced using first, second, and third strings of LEDs
that respectively generate green, red, and blue light, current
through each LED string may be individually controlled to control
the brightness and/or color temperature of the white light.
[0080] Conventionally, current through each LED string is
controlled by using a Buck converter operated in current mode.
Controlling current using a Buck converter in each LED string,
however, requires at least one inductor and one capacitor per LED
string and additional external components including resistors.
Further changes in brightness need to be communicated to the
current controller, which requires additional components. These
additional components increase cost.
[0081] The present disclosure relates to current balancing circuits
that control current through LEDs without using inductors.
Specifically, the current balancing circuits according to the
present disclosure maintain currents through a plurality of LED
strings at a predetermined proportion and output white light of a
predetermined color temperature. The current balancing circuits
maintain the currents at the predetermined proportion regardless of
an increase or decrease in the amount of power supplied to the LED
strings (e.g., when a user changes the brightness level). When the
power increases (e.g., to make the white light brighter), the
current balancing circuits increase currents through the LED
strings in the same predetermined proportion. When the power
decreases (e.g., to make the white light dimmer), the current
balancing circuits decrease currents through the LED strings in the
same predetermined proportion to maintain the whiteness of the
light. However, a predetermined set of values for the currents
through the LED strings can also be used to match the color of the
light emitted by an incandescent or a halogen light bulb. Making
the light more reddish while dimming is similar to natural sun
light. Also, light emitted by incandescent bulbs becomes more
yellowish at lower power, and such light is more pleasing to human
eye.
[0082] The disclosure is organized as follows. Before discussing
the current balancing circuits, in FIGS. 1-6B, examples of
LED-based lamps where the current balancing circuits can be used
are described. Specifically, in FIGS. 1 and 2, a general LED-based
lamp according to the present disclosure is described. In FIGS.
3A-4B, an LED-based lamp that has a shape of a conventional light
bulb and that comprises a color temperature control switch
according to the present disclosure is described. In FIGS. 5A and
6B, an LED-based lamp for illuminating large areas (e.g., a
LED-based tube light) comprising a color temperature control switch
according to the present disclosure is described. In FIG. 7, a
general current balancing circuit that uses current mirroring and
feedback to balance currents through two loads is described. For
example, the two loads may include two strings of LEDs respectively
producing light of two different colors that combines to generate
white light. In FIG. 8, a current mirror circuit that uses current
mirroring to balance currents through a plurality of LED strings is
described. In FIG. 9, a current balancing circuit that uses current
mirroring and feedback to balance currents through a plurality of
LED strings is described. In FIG. 10, a method for controlling
current through a plurality of LED strings in one or more LED lamps
is described. In FIGS. 11A-12B, additional arrangements of LEDs and
phosphors are shown.
[0083] Referring now to FIG. 1, an LED lamp 100 according to the
present disclosure is shown. The LED lamp 100 includes a power
converter module 102 and a set of LEDs 104. The power converter
module 102 converts AC power to DC power. The power converter
module 102 supplies the DC power to the LEDs 104.
[0084] The LEDs 104 may include a plurality of strings of LEDs. A
detailed discussion of the plurality of strings of the LEDs 104
follows with references to FIGS. 4 and 6. Each string of LEDs may
include a set of LEDs connected in series as shown in FIGS. 4 and
6. For example, as shown in FIG. 4, the LEDs 104 may include a
first string of blue LEDs, a second string of blue LEDs coated with
a green phosphor, and a third string of LEDs coated with a red
phosphor.
[0085] In lamps using three LED strings as shown in FIG. 4 (e.g.,
see FIG. 3A), the first string of blue LEDs may not be coated with
a phosphor that converts blue light to a light of a different
color. Alternatively, the first string of blue LEDs may be coated
with an amber phosphor. The amber phosphor may convert a portion of
the blue light emitted by the third string of blue LEDs to red
light and allow a remainder of the blue light emitted by the third
string of blue LEDs to escape unconverted. The green and red light
generated by the second and third strings of LEDs and the blue (and
red) light generated by the first string of LEDs combine to
generate white light.
[0086] Alternatively, as shown in FIG. 6, the LEDs 104 may include
first and second strings of blue LEDs. In lamps using the LED
strings shown in FIG. 6 (e.g., see FIGS. 5A and 5B), a glass
surface may be coated with green and red phosphors to convert the
blue light emitted by the first and second strings of LEDs
respectively to green and red light. The LEDs and the coatings of
green and red phosphors are arranged in a manner to allow some of
the blue light emitted by the LEDs in the first and second strings
to escape unconverted by the green and red phosphors. The green and
red light generated by the first and second strings of LEDs
combines with the blue light that escapes unconverted to generate
white light.
[0087] Referring now to FIG. 2, the power converter module 102 may
include a power supply module 106 and a current control module 108.
The power supply module 106 converts the AC power to the DC power.
For example, the power supply module 106 may include a
switched-mode power supply that converts the AC line voltage to a
DC voltage and a DC-to-DC converter that converts the DC voltage to
a voltage V.sub.out suitable to power the LEDs 104.
[0088] The current control module 108 controls current through the
LEDs 104. The current control module 108 uses one of the current
balancing circuits according to the present disclosure to control
current through the LEDs 104. The amount of current supplied to the
LEDs 104 may be predetermined. For example, the amount of current
supplied to each LED string may be predetermined to produce light
having a predetermined whiteness (also called color temperature).
The predetermined current may be programmed in the current control
module 108 at the time of manufacture. However, according to the
present disclosure, the total current is not controlled by the
current control module 108. Instead, a current balancer divides the
incoming current to the multiple LED strings in a predetermined
ratio. The ratio is fixed at the time of manufacture to produce
white light of desired color temperature.
[0089] In some implementations, the current control module 108 may
receive feedback from the LEDs 104. For example, the feedback may
include voltages across the plurality of strings of the LEDs 104.
Based on the feedback, the current control module 108 may change
the current through one or more strings of the LEDs 104 to maintain
the predetermined whiteness of the light.
[0090] In some implementations, the current control module 108 may
receive an input from a user-controllable switch located on the LED
lamp 100. For example, when the LED lamp 100 has the shape of a
standard light bulb that screws into a receptacle, a switch may be
located at a base portion of the LED lamp 100, which screws into
the receptacle. When the LED lamp 100 has the shape of a tube light
or any other large area lamp, the switch may be located on a lamp
holder, a base portion, or any other suitable location on the LED
lamp 100. Based on the input, the current control module 108 may
change the whiteness (i.e., color temperature) of the white light
produced by the LEDs 104.
[0091] For example, using the switch, the user may select one of
four color temperatures (in degrees Kelvin): 4000K, 3500K, 3000K,
and 2700K. Additionally, the user may be able to select any value
between 4000K and 2700K. White light in the 3500-4000K temperature
range is called neutral white light. White light in the 2700-3000K
temperature range is called warm white light. Warm white light has
a yellow hue. White light in the 4500-5500K temperature range is
called cool white light. Cool white light has a bluish hue. Using
the switch, the user can change the color temperature of the white
light generated by the LED lamp 100 without changing the LED lamp
100.
[0092] Referring now to FIGS. 3A and 3B, an example of an LED lamp
10 comprising a temperature control switch according to the present
disclosure is shown. In FIG. 3A, the LED lamp 10 includes a base
portion 12 and a light dispersing portion 14. The base portion 12
screws into a receptacle. The light dispersing portion 14 includes
the power control module 102, the LEDs 104, and an optical
reflector assembly (not shown). The portions 12 and 14 are a single
piece. A small ring 18 is mounted around the neck of the LED lamp
10. The ring 18 slides over the body of the LED lamp 10. The ring
18 is connected to a switch inside the body of the LED lamp 10 to
control the whiteness (i.e., the color temperature) of the light
output by the LED lamp 10. Hereinafter the ring 18 and the switch
are collectively referred to as the temperature control switch
18.
[0093] For example, the temperature control switch 18 can have one
of a plurality of states (e.g., A, B, C, or D). Each state can
correspond to a different color temperature between 2700 and 5500
degrees Kelvin. The states can be marked on the base portion 12,
and an indicator 16 on the light dispersing portion 14 can indicate
the state selected by rotating the light dispersing portion 14.
Alternatively, the indicator 16 can be located on the base portion
12, and the markings of the states can be located on the light
dispersing portion 14. By rotating the temperature control switch
18 to different positions, the user can select different color
temperatures.
[0094] The power converter module 102 is included in the light
dispersing portion 14 of the LED lamp 10. In some implementations,
the power converter module 102 may be included in the base portion
12 of the LED lamp 10 instead of in the light dispersing portion 14
of the LED lamp 10. The power converter module 102 senses a state
of the temperature control switch 18. Based on the state of the
temperature control switch 18, the power converter module 102
adjusts the DC power supplied to the LEDs 104.
[0095] In FIG. 3B, a functional block diagram of an LED lamp 10
comprising a temperature control switch according to the present
disclosure is shown. The LED lamp 10 includes the power converter
module 102, the LEDs 104, and the temperature control switch 18.
The power converter module 102 includes the power supply module 106
and a color temperature adjustment module 109. The color
temperature adjustment module 109 includes the current control
module 108 and a sensing module 110.
[0096] The color temperature adjustment module 109 adjusts or
varies outputs of the first, second, and third sets of LEDs 104
according to a color temperature selected by a user using the
temperature control switch 18. For example, the current control
module 108 adjusts or varies currents through the first, second,
and third sets of LEDs 104 according to a color temperature
selected by a user using the temperature control switch 18. While
current control is described as a way of adjusting or varying
outputs of the first, second, and third sets of LEDs 104, other
ways (e.g., voltage control, power control, and so on) may be used
to adjust or vary outputs of the first, second, and third sets of
LEDs 104.
[0097] The sensing module 110 senses the state of the temperature
control switch 18 selected by the user. Based on the sensed state,
the power converter module 102 selects a corresponding color
temperature and adjusts the DC power supplied to the LEDs 104.
Specifically, the sensing module 110 outputs a signal to the
current control module 108 based on the sensed state. The current
control module 108 controls current through the LEDs 104 according
to the sensed state to output white light having a corresponding
color temperature.
[0098] For example, the current control module 108 may select
currents through the LED strings having a first proportion when the
temperature control switch 18 is in a first position, a second
proportion when the temperature control switch 18 is in a second
position, and so on. For example, currents through first, second,
and third strings may be in proportion X1:Y1:Z1 when the
temperature control switch 18 is in the first position; X2:Y2:Z2
when the temperature control switch 18 is in the second position;
and so on. X1, Y1, Z1, X2, Y2, Z2, and so on are numbers. For
example, X1:Y1:Z1 may be 1:2:3; X2:Y2:Z2 may be (1.1):(2.4):(3.8);
and so on. For example, X1:Y1:Z1 may be 1:2:3; X2:Y2:Z2 may be
(0.9):(2.2):(3.6); and so on.
[0099] Referring now to FIG. 4, an example of a plurality of
strings of the LEDs 104 using in the LED lamp 10 is shown. For
example only, three strings: a first string 112, a second string
114, and a third string 116 are shown. For example, the first
string 112 may include blue LEDs without a phosphor coating to
convert blue light into a light of a different color; the second
string 114 may include blue LEDs with a coating of green phosphor;
and the third string 116 may include blue LEDs with a coating of
red phosphor. Additional or fewer strings having LEDs coated with
different phosphors may be used. Multiple strings (e.g., two or
more strings) of each of the first string 112, the second string
114, and the third string 116 may be used. For example only, five
LEDs are shown in each LED string. Fewer or more than five LEDs may
be used in each LED string.
[0100] In some implementations, LEDs in the first string 112 may be
coated with an amber phosphor. The current control module 108
controls currents through the first string 112, the second string
114, and the third string 116 to generate white light having a
desired whiteness (i.e., color temperature).
[0101] The LEDs in the first string 112 may emit blue light having
a set of wavelengths approximately around 450 nm (e.g., between
450-470 nm). The LEDs in the second string 114 may emit blue light
having wavelengths less than 450 nm. The LEDs in the third string
116 may emit blue light having wavelengths greater than 470 nm. The
blue LEDs producing blue light having the highest wavelength (e.g.,
greater than .about.470 nm) should be used with red/amber phosphor
to minimize losses due to Stokes' shift. Similarly, the blue LEDs
producing blue light having lower wavelengths are to be used with
green phosphor.
[0102] The currents supplied by the current control module 108
determine the amount of blue (and red) light generated by the LEDs
in the first string 112, the amount of green light generated by the
LEDs in the second string 114, and the amount of red light
generated by the LEDs in the third string 116. The current control
module 108 may reduce the amount of current through the third
string 116 in proportion to the amount of red light produced by the
LEDs in the first string 112 when coated with the amber
phosphor.
[0103] Additionally, the current control module 108 may adjust the
proportion of currents through the first string 112, the second
string 114, and the third string 116 depending on the color
temperature selected by the user. The blue (and red) light output
by the LEDs in the first string 112, the green light output by the
LEDs in the second string 114, and the red light output by the LEDs
in the third string 116 combine to generate white light of desired
whiteness.
[0104] In some implementations, a brightness control (e.g. a dimmer
switch) may be connected to the LED lamp 10. The power converter
module 102 may receive the AC power according to a setting of the
dimmer switch. The power supply module 106 may output different
amounts of DC power based on the settings of the dimmer switch.
Based on the amount of DC power received from the power supply
module 106, the current control module 108 may change currents
through one or more strings of the LEDs 104. The brightness of the
white light output by the LEDs 104 may change based on the changes
in the currents through the LEDs 104.
[0105] The current control module 108 may change currents through
one or more strings of the LEDs 104 according to a dimmer variable
(e). For example, the currents through one or more strings of the
LEDs 104 may be in proportion X1:Y1:Z1. For example, the current
control module 108 may change currents through one or more strings
of the LEDs 104 from 0.5:0.5:0.5 to 1.5:1.5:1.5.
[0106] Referring now to FIGS. 5A and 5B, an example of an LED lamp
150 for illuminating large areas according to the present
disclosure is shown. For example only, the LED lamp 150 having the
shape of a tube light is shown. The teachings disclosed herein with
reference to the LED lamp 150 can be applied to any LED lamp used
to illuminate large areas.
[0107] In FIG. 5A, the LED lamp 150 includes a base portion 154 and
a glass layer 156. LEDs 104 are arranged on the base portion 154 as
described below in detail. An inner surface of the glass layer 156
that faces the LEDs 104 is coated with phosphors 158 as explained
below in detail. The base portion 154 and the glass layer 156
terminate on either side in a lamp holder 160. Each lamp holder 160
connects to a receptacle via bi-pin fittings 162. The base portion
154 includes the power converter module 102. The power converter
module 102 is connected to the bi-pin fittings 162. The power
converter module 102 receives AC power via the bi-pin fittings 162.
The power converter module 102 converts AC power into DC power and
supplies the DC power to the LEDs 104. A transparent or opaque
material 157 may be used to cover the glass layer 156. In some
implementations, instead of the glass layer 156, a layer of any
other suitable (e.g., transparent) material may be used.
[0108] In FIG. 5B, the placement of the LEDs 104 and phosphors 158
is shown in detail. A plurality of LEDs 104-1, 104-2, . . . , 104-n
(collectively LEDs 104), where n is an integer greater than 1, is
arranged on the base portion 154. The LEDs 104 include two sets of
LEDs. A first set of LEDs generates blue light having a first
wavelength. A second set of LEDs generates blue light having a
second wavelength. For example only, the first wavelength is less
than or equal to 450 nm, and the second wavelength is greater than
or equal to 470 nm. In some implementations, the first wavelength
may be 450 nm.+-.X nm, and the second wavelength may be 470 nm.+-.X
nm, where 0.ltoreq.X.ltoreq.20, for example. The number X can also
be greater than 20.
[0109] The LEDs 104 in the first and second sets are evenly spaced
and arranged in an alternating pattern along a straight line on the
base portion 154. For example, the LEDs 104-1, 104-3, and so on
belong to the first set of LEDs; and the LEDs 104-2, 104-4, and so
on belong to the second set of LEDs. The LED 104-1 is separated by
a distance d1 from the LED 104-2; the LED 104-2 is separated by the
distance d1 from the LED 104-3; and so on.
[0110] The inner surface of the glass layer 156 facing the LEDs 104
includes a plurality of coatings of phosphors 158. For example, the
coatings of phosphors 158 include coatings of green and red
phosphors. Each coating of green and red phosphors may be of a
length L. In some implementations, the coatings of green and red
phosphors may have different lengths. The coatings of green and red
phosphors are arranged in an alternating pattern along a straight
line on the inner surface of the glass layer 156. While the
coatings of green and red phosphors are contiguous, in some
implementations, the coatings may be separated by a gap. Centers of
the green phosphors are aligned with centers of the first set of
LEDs. Centers of the red phosphors are aligned with centers of the
second set of LEDs. The glass layer 156 is separated by a distance
d2 from the base portion 154.
[0111] The green phosphors convert some of the blue light emitted
by the first set of LEDs to green light. The red phosphors convert
some of the blue light emitted by the second set of LEDs to red
light. Some of the blue light emitted by the first and second set
of LEDs escapes the phosphors 158 unconverted. The placement of the
LEDs 104 and the phosphors 158 described above allows a first
portion of the blue light emitted by the LEDs 104 to be converted
by the phosphors 158 to green and red light and allows a second
portion of the blue light emitted by the LEDs 104 to escape
unconverted. The green light, the red light, and the escaped blue
light combine to form white light.
[0112] The amount of blue light that escapes the phosphors 158 may
depend on various factors. For example, the factors may include
values of the first and second wavelengths, a density of coatings
of the green and red phosphors 158, the length L of each coating of
the green and red phosphors 158, a length of a gap between adjacent
phosphor coatings, the distance d1 between the LEDs 104, the
distance d2 between the base portion 154 and the glass layer 156,
and so on. The uniformity of the white light across the LED lamp
150 may also depend on one or more of these factors.
[0113] A functional block diagram of the LED lamp 150 shown in
FIGS. 5A and 5B is similar to the functional block diagram of the
LED lamp 10 shown in FIG. 3B and is therefore not shown and
described again to avoid repetition.
[0114] Referring now to FIG. 6, an example of a plurality of
strings of the LEDs 104 used in the LED lamp 150 is shown. For
example only, two strings: a first string 114 and a second string
116 are shown. For example only, five LEDs are shown in each LED
string. Fewer or more than five LEDs may be used in each LED
string. For example, the first string 114 may include LEDs that
emit blue light having the first wavelengths, and the second string
116 may include LEDs that emit blue light having the second
wavelengths. For example, the LEDs in the first string 114 may emit
blue light having a set of wavelengths approximately around 450 nm
(e.g., 450 nm.+-.X nm). The LEDs in the second string 116 may emit
blue light having a set of wavelengths approximately around 470 nm
(e.g., 470 nm.+-.X nm). For example only, 0.ltoreq.X.ltoreq.20, for
example. The number X can also be greater than 20.
[0115] The currents supplied by the current control module 108
determine the amount of blue light generated by the LEDs in the
first string 114 and the second string 116. The current control
module 108 may adjust the proportion (i.e. ratio) of currents
through the first string 114 and the second string 116 depending on
the color temperature selected by the user. The blue light output
by the LEDs in the first string 114 and the second string 116 is
partly converted by the phosphors 158 into green and red light and
partly allowed to escape unconverted. The green and red light
converted by the phosphors 158 combines with the unconverted blue
light to generate white light of desired whiteness.
[0116] In some implementations, a brightness control (e.g. a dimmer
switch) may be connected to the LED lamp 150. The power converter
module 102 may receive the AC power according to a setting of the
dimmer switch. The power supply module 106 may output different
amounts of DC power based on the settings of the dimmer switch.
Based on the amount of DC power received from the power supply
module 106, the current control module 108 may change currents
through one or more strings of the LEDs 104. The brightness of the
white light output by the LEDs 104 may change based on the changes
in the currents through the LEDs 104.
[0117] Referring now to FIG. 7, a current balancing circuit 200
according to the present disclosure is shown. The current balancing
circuit 200 maintains currents through multiple loads at a
predetermined proportion (i.e., ratio). For example only, the
current balancing circuit 200 is shown to include only two loads,
L1 and L2. The current balancing circuit 200, however, can maintain
currents through any number of loads at a predetermined proportion.
Further, while the current balancing circuit 200 is discussed
herein with reference to LED strings as loads, the current
balancing circuit 200 can be used to balanced currents through
other loads.
[0118] The current balancing circuit 200 senses a change in current
through one of the loads and adjusts currents through the other
load(s) so that the currents through the loads are in a
predetermined proportion despite the change in current through one
of the loads. For example, if the loads receive more (or less)
power (e.g., V.sub.out from the power supply module 106), the
current balancing circuit 200 increases (or decreases) currents
through the loads to maintain the currents at the predetermined
proportion. When the loads include LED strings that output light of
different colors to produce white light, the current balancing
circuit 200 maintains the proportion of the currents through the
LED strings to the predetermined ratio regardless of changes in
brightness made by a user. The current balancing circuit 200
maintains the ratio of the currents. The color of the light
produced depends on other factors as well.
[0119] The current balancing circuit 200 comprises transistors
M1-M8, loads L1 and L2, and resistors R1 and R2 connected as shown
in FIG. 7. The loads L1 and L2 are respectively connected to drains
D5 and D6 of the drivers M5 and M6. The gates of the drivers M5 and
M6 are connected to an output of a comparator comprising
transistors M1, M2, and M3. Transistors M7 and M8 form a current
mirror. The current mirror is connected to the comparator as shown.
For example only, the loads L1 and L2 may respectively include two
strings of LEDs configured to generate light of two different
colors that combines to produce white light of a predetermined
color temperature (e.g., see FIG. 6). While not shown, additional
loads and drivers may be added, and the comparator may be modified
accordingly. (For example, see FIG. 9.)
[0120] The current balancing circuit 200 compares the lowest of the
voltages V1 or V2 at the drains D5 and D6 of the transistors M5 and
M6 to a reference voltage V.sub.ref. The voltages V1 and V2 are
kept substantially equal to or above at least a certain value, such
that currents through the transistors M5, M6, M7, and M8 are
matched to the best possible accuracy. Even with perfectly matched
transistors M5 and M6, if there is difference in the loads L1 and
L2, the difference might cause the voltages V1 and V2 to be
different from each other. By controlling a gate voltage V.sub.g of
the transistors M5 and M6, the current balancing circuit 200
ensures that both the voltages V1 and V2 are at least
V.sub.ref.
[0121] If voltages V1 and V2 at the drains D5 and D6 of the
transistors M5 and M6 closely match, currents through the
transistors M5 and M6 (and hence through the loads L1 and L2) are
proportional to respective areas of transistors M5 and M6. The
comparator compares the lowest of the voltages V1 and V2 at the
drains D5 and D6 to the reference voltage V.sub.ref. The voltages
V1 and V2 at the drains D5 and D6 may become different due to a
change in current through one of the loads. For example, current
through one of the loads may change due to a change in V.sub.out
delivered by the power converter module 102 when a user changes
brightness level. The comparator adjusts the gate voltage V.sub.g
of the transistors M5 and M6 until the voltages V1 and V2 at the
drains D5 and D6 are at least V.sub.ref. This makes the ratio of
currents through the loads L1 and L2 proportional to the ratio of
the areas of the transistors M5 and M6. When V1 or V2 changes, the
comparator compares the lowest of the voltages V1 or V2 to
V.sub.ref and generates V.sub.g based on the comparison. V.sub.g
drives the gates of M5 and M6 to change currents through the loads
L1 and L2 so that the currents are proportional to the ratio of the
areas of the transistors M5 and M6. When the output voltage
V.sub.out across the loads changes (e.g., due a change in the
brightness level by a user), the current balancing circuit 200
adjusts the currents through the loads L1 and L2 to maintain the
currents at a predetermined ratio.
[0122] For example, suppose that current through one of the loads
L1 or L2 decreases due to a change in brightness level by the user.
Due to a decrease in current through load L1 or L2, the voltage V1
or V2 decreases. If the voltage V1 at D5 decreases, more current
flows into transistor M2. If the voltage V2 at D6 decreases, more
current flows into transistor M3. If current through transistor M2
or M3 increases, current through transistor M7 increases. Due to
current mirroring, current through transistor M8 increases. The
increased current through transistor M8 pulls the gates of
transistors M5 and M6 to a lower voltage V.sub.g. Lowering the
voltage V.sub.g at the gates of transistors M5 and M6 decreases
currents through the loads connected to the respective drains.
[0123] In this manner, if current through the load L1 changes, the
current balancing circuit 200 changes the current through the load
L2 to track the change in current through the load L. If current
through the load L1 increases (or decreases), the current balancing
circuit 200 adjusts the gate drive V.sub.g of the transistors M5
and M6 to increase (or decrease) current through the load L2 in the
same proportion. Accordingly, the ratio of currents through the
loads L1 and L2 is maintained at a predetermined value.
Consequently, the color temperature of the white light output by
the LEDs (loads L1 and L2) is maintained at a predetermined
value.
[0124] Referring now to FIG. 8, an example of a current mirror
circuit 250 that drives three strings of LEDs is shown. Suppose
that the three LED strings respectively produce blue, green, and
red light that combines to generate white light. The current mirror
circuit 250 includes transistors M5, M6, and M7 that respectively
drive the three LED strings. The current mirror circuit 250
controls the ratio of currents through the three LED strings
proportional to the area of the transistors M5, M6, and M7. For
example, if a proportion of the areas A1, A2, and A3 of the
transistors M5, M6, and M7 is 1:2:3, the currents through the blue,
green and red LED strings will be in the proportion 1:2:3.
[0125] To accurately control the proportion of currents, the drain
voltages of the transistors M5, M6, and M7 need to closely match.
If the three LED strings use pure blue, pure green, and pure red
LEDs, the drain voltages of the transistors M5, M6, and M7 may not
closely match due to differences in voltage/current characteristics
of materials used to manufacture the pure blue, green, and red
LEDs. Instead, if a combination of blue LEDs and phosphors is used
in the three LED strings to generate blue, green, and red light,
the voltage/current characteristics of the three LED strings will
closely match since the blue LEDs in each string are made from the
same material. Accordingly, the drain voltages of the transistors
M5, M6, and M7 will closely match. For the same amount of current,
the voltage across the LED strings will be similar, and hence the
drain voltages of the transistors M5, M6, and M7 will be close to
each other. Consequently, the proportion of currents through the
three LED strings will be accurate.
[0126] When V.sub.out changes, however, the current mirror circuit
250 includes no feedback mechanism to detect changes in currents
through the LED strings and to adjust gate drive (i.e., biasing) of
the transistors M5, M6, and M7 based on the changes in V.sub.out.
Accordingly, the current mirror circuit 250 cannot adjust the gate
drive of the transistors M5, M6, and M7 in response to changes in
V.sub.out. Consequently, when V.sub.out increases, the voltage drop
across the transistors M5, M6, and M7 will increase resulting in an
increase in power dissipation.
[0127] Further, to change brightness level, when reference current
I1 is changed, the ratio of currents through the three LED strings
may need to be changed. For example, for a first value of 11,
currents through the three LED strings may need to have a ratio of
X1:Y1:Z1 to produce white light of a predetermined color
temperature (whiteness); for a second value of 11, currents through
the three LED strings may need to have a ratio of X2:Y2:Z2 to
produce white light of the predetermined color temperature; and so
on. For example, the ratio X1:Y1:Z1 may be 1:2:3; and the ratio
X2:Y2:Z2 may be 1:2:2, or 2:1:3, and so on. This is because the
conversion efficiencies of the phosphors may differ at different
currents. The ratio will need to be changed particularly if current
through one of the three LED strings differs from currents through
the other LED strings by a large amount (e.g., if the currents are
in proportion 1:2:3). If the ratio is not changed when I1 is
changed, the color temperature of the white light will change.
Therefore, to get the desired color when I1 is changed, the ratio
of the currents will need to be changed, particularly when current
through one of the LED strings required to produce a predetermined
whiteness differs largely from other currents required to produce
the predetermined whiteness.
[0128] Referring now to FIG. 9, a current balancing circuit 300
includes a comparator and a current mirror to sense the drain
voltages of the transistors M5, M6, and M7 and to adjust the gate
voltage V.sub.g of the transistors M5, M6, and M7 when V.sub.out
changes. The comparator and the current mirror of the current
balancing circuit 300 are similar to the comparator and the current
mirror of the current balancing circuit 200 shown in FIG. 7.
[0129] The current balancing circuit 300 increases the gate voltage
V.sub.g of the transistors M5, M6, and M7 when V.sub.out increases.
Increasing the gate voltage V.sub.g of the transistors M5, M6, and
M7 in response to an increase in V.sub.out reduces power
dissipation of the transistors M5, M6, and M7. Additionally, the
current balancing circuit 300 decreases the gate voltage V.sub.g of
the transistors M5, M6, and M7 when V.sub.out decreases. Decreasing
the gate voltage V.sub.g of the transistors M5, M6, and M7 in
response to a decrease in V.sub.out increases the drain voltages
V1-V3 of the transistors M5, M6, and M7 to levels that are
comparable to the reference voltage V.sub.ref.
[0130] As explained with reference to FIG. 7, a comparator
comprising transistors M1, M3, M3, and M10 compares voltages V1-V3
at the drains D5-D7 of the transistors M5-M7 to the reference
voltage V.sub.ref. When current through one of the three LED
strings changes, the comparator and the current mirror comprising
transistors M9 and M8 adjust the gate voltage V.sub.g (i.e.,
biasing) of the transistors M5-M7 to change the currents through
the remaining LED strings to maintain a predetermined ratio of the
currents through the three LED strings.
[0131] If the voltages V1-V3 at the drains D5-D7 of the transistors
M5-M7 closely match, currents through the transistors M5-M7 (and
hence through the three LED strings) are proportional to respective
areas of transistors M5-M7. For example, if a proportion of the
areas A1, A2, and A3 of the transistors M5, M6, and M7 is 1:2:3,
the currents through the blue, green, and red LED strings will be
in the proportion 1:2:3. The comparator compares the voltages V1-V3
at the drains D5-D7 to the reference voltage V.sub.ref. The
voltages V1-V3 at the drains D5-D7 may become different due to a
change in current through one of the loads. For example, current
through one of the loads may change due to a change in V.sub.out
delivered by the power converter module 102 when a user changes
brightness level. The comparator adjusts the gate voltage V.sub.g
of the transistors M5-M7 until the lowest voltage of V1, V2, and V3
at the drains D5, D6, and D7 closely match the V.sub.ref. This
makes the ratio of currents through the three LED strings
proportional to the ratio of the areas of the transistors M5-M7.
When V1 or V2 or V3 changes, the comparator compares V1 or V2 or V3
is compared to V.sub.ref and generates V.sub.g based on the
comparison. V.sub.g drives the gates of M5-M7 to change the
currents through the three LED strings so that the currents are
proportional to the ratio of the areas of the transistors M5-M7.
When the output voltage V.sub.out across the three LED strings
changes (e.g., due a change in the brightness level by a user), the
current balancing circuit 300 adjusts the currents through the
three LED strings to maintain the currents at a predetermined
ratio.
[0132] For example, suppose the current through one of the three
LED strings decreases due to a change in brightness level by the
user. Due to a decrease in current through one of the three LED
strings, the voltage V1 or V2 or V3 decreases. If the voltage V1 at
D5 decreases, more current flows into transistor M2. If the voltage
V2 at D6 decreases, more current flows into transistor M3. If the
voltage V3 at D7 decreases, more current flows into transistor M10.
If current through transistor M2 or M3 or M10 increases, current
through transistor M9 increases. Due to current mirroring, current
through transistor M8 increases. The increased current through
transistor M8 pulls the gates of transistors M5-M7 to a lower
voltage V.sub.g. Lowering the voltage V.sub.g at the gates of
transistors M5-M7 decreases currents through the three LED strings
connected to the respective drains.
[0133] In this manner, if the total current through the three LED
string changes, the current balancing circuit 300 changes the
currents through one or more of the three LED strings to track the
change. Accordingly, the ratio of currents through the three LED
strings is maintained at a predetermined value. Consequently, the
color temperature of the white light output by the three LED
strings is maintained at a predetermined value.
[0134] In one implementation, for example, the currents through the
three LED strings required to produce white light of a
predetermined color temperature may be known during manufacture. If
the currents through the three LED strings are vastly different
(e.g., if the currents through the red, green, and blue LED strings
are in a ratio 3:2:1), the transistors M5-M7 can be designed to
have area with the same ratio as the currents. Accordingly, for the
same gate drive V.sub.g, the drain voltages of the transistors
M5-M7 will closely match. For example, the transistor M7 driving
the LED string producing red light at 180 mA will have the same
drain voltage as the transistor M6 driving the LED string producing
green light at 120 mA and the transistor M5 driving the LED string
producing blue light at 60 mA.
[0135] Alternatively, the LEDs may be designed so that the area of
the transistors M5-M7 and currents through the three LED strings
can be equal, and the drain voltages of the transistors M5-M7
closely match. For example, suppose that 180, 120, and 60 units of
red, green, and blue light are respectively required to produce
white light of a predetermined color temperature. The LED string
producing pure red light may be supplied less current (e.g., 120 mA
instead of 180 mA) to produce only 120 units of red light instead
of producing 180 units of red light. Additionally, the LEDs in the
blue string producing blue light may be coarsely coated with amber
or red phosphor so that half of the blue light is converted to red
light and half of the blue light escapes unconverted. The LED
string producing a mixture of red and blue light may be supplied a
higher current (e.g., 120 mA instead of 60 mA) to produce 120 units
of light including 60 units each of red and blue light. The LED
string producing pure green light may be supplied the same current
as the other LED strings (e.g., 120 mA) to produce 120 units of
green light. In this manner, all three LED strings can be supplied
with the same current (e.g., 120 mA) and can produce the required
amounts of red, green, and blue light to produce white light of
desired whiteness. The transistors M5-M7 can have the same area and
produce drain voltages that closely match.
[0136] In illumination systems using AC-to-DC converters, a
brightness control signal (also called dimming signal) is typically
provided by the primary side (the AC side). Communicating the
dimming signal from the primary side to the secondary side (where
the current balancing circuit operates) can be difficult due to
isolation between the primary and secondary sides and due to safety
standards and regulations. Often additional circuitry is required
to communicate the dimming signal from the primary side to the
secondary side.
[0137] The current balancing circuits disclosed herein do not
require the dimming signal to be transmitted from the primary side.
Instead, when the primary side delivers more current than the total
current in the LED strings (e.g., 180+120+60=360 mA in the above
example), the output voltage V.sub.out increases. The current
balancing circuit adjusts the gate drive of the transistors driving
the LED strings to increase the currents through the LED strings
and maintains the ratio between the currents to output white light
of the desired color temperature.
[0138] Referring now to FIG. 10, a method 400 for balancing
currents through LED strings according to the present disclosure is
shown. At 402, control supplies current at a predetermined ratio to
a plurality of LED strings to produce white light of a
predetermined color temperature. At 404, control determines whether
input power to the plurality of LED strings has changed. At 406, if
the input power to the plurality of LED strings has changed,
control adjusts gate voltages of transistors that drive the LED
strings and changes currents through the LED strings to maintain
the predetermined ratio between the currents. Accordingly, control
maintains the predetermined color temperature of the white light
produced by the plurality of LED strings regardless of changes in
the input power to the plurality of LED strings.
[0139] In one application, the current balancing disclosed herein
is used to manage the distribution of the blue spectrum. In
particular, the human eye is sensitive only to a certain range of
blue wavelengths. For example, the human is not very sensitive to
blue wavelengths of less than or equal to 450 nm. Rather, the human
eye sees normal blue at approximately 470 nm. Accordingly, blue
LEDs producing blue light having wavelengths of about 470 nm are
used to produce blue light, and blue LEDs producing blue light of
other wavelengths are used to convert to green and red light. For
example, the blue LEDs producing blue light having wavelengths
between 440 and 460 nm can be used to convert to green light, and
the blue LEDs producing blue light having wavelengths greater than
470 nm can be used to convert to red light.
[0140] White light can be generated in different ways. For example,
white light can be generated using a combination of blue light
generated by blue LEDs, and blue light converted to green and red
light. Alternatively, white light can also be generated using a
combination of blue light and blue light converted to yellow and
reddish yellow light.
[0141] Since human eye is sensitive to variations in wavelength in
a certain range of the blue spectrum, blue light used in producing
white light need not be generated using LEDs that produce blue
light. Instead, blue light used in producing white light can be
generated by converting ultraviolet light to broadband blue light.
Only a small amount of ultraviolet light needs to be converted to
blue light since only a small amount of blue light (e.g., 5-10%) is
needed to produce white light. Other colors needed to produce white
light, such as green, red, yellow, or reddish yellow, can be
generated by converting blue light produced by blue LEDs having
varying wavelengths (and therefore varying shades of blue) in the
blue spectrum.
[0142] Thus, blue light in the entire range of the blue spectrum
(i.e., light produced by blue LEDs having all the blue wavelengths)
is used to convert to one or more of the other colors, and none of
the blue color generated by the blue LEDs is used in producing
white light. Accordingly, when blue LEDs are manufactured, blue
LEDs that produce blue light having wavelengths that are useful
and/or optimal in some applications (e.g., 470 nm) can be sold and
utilized in those applications, and blue LEDs that produce blue
light having other varying wavelengths in the not so useful or
suboptimal range can be used to convert to other colors used in
producing white light. This improves the yield of blue LEDs in the
manufacturing process, and minimizes the percentage of the
manufactured blue LEDs that are not utilized.
[0143] Further, blue LEDs can be optimized to produce blue light
having wavelengths to which human eye is not very sensitive (e.g.,
from 440 to 460 nm). For example, blue LEDs can be optimized to
generate blue light having a wavelength of 450 nm. Blue LEDs
producing blue light having not so useful or suboptimal wavelengths
in the blue spectrum (e.g., 430 to 460 nm), to which human eye is
not very sensitive, can be utilized to convert to green or red or
other colors. One or more of these colors can be combined with the
blue light generated by converting ultraviolet light to produce
white light. In other words, blue LEDs can be intentionally
manufactured to produce blue light having not so useful or
suboptimal wavelengths in the blue spectrum (e.g., 430 to 460
nm).
[0144] Referring now to FIGS. 11A-11D, different ways of producing
white light having different whiteness (i.e., different color
temperatures) are shown. In FIG. 11A, blue light emitted by blue
LEDs having wavelength of about 450 nm (for example) can be
converted to red and green light using red and green phosphors.
Ultraviolet light emitted by ultraviolet LEDs having wavelength of
less than or equal to 400 nm can be converted to blue light using
the blue phosphor. The red, green, and blue light can be combined
to produce white light. Current through the LEDs used to generate
one or more of red, green, and blue color can be adjusted to adjust
the color temperature of the white light.
[0145] In FIG. 11B, blue light emitted by blue LEDs having
wavelength of about 450 nm (for example) can be converted to
reddish yellow and yellow light using reddish yellow and yellow
phosphors. Ultraviolet light emitted by ultraviolet LEDs having
wavelength of less than or equal to 400 nm can be converted to blue
light using the blue phosphor. The reddish yellow, yellow, and blue
light can be combined to produce white light. Current through the
LEDs used to generate one or more of reddish yellow, yellow, and
blue color can be adjusted to adjust the color temperature of the
white light.
[0146] In FIG. 11C, blue light emitted by blue LEDs having
wavelength of about 450 nm (for example) can be converted to red
and yellow light using red and yellow phosphors. Ultraviolet light
emitted by ultraviolet LEDs having wavelength of less than or equal
to 400 nm can be converted to blue light using the blue phosphor.
The red, yellow, and blue light can be combined to produce white
light. Current through the LEDs used to generate one or more of
red, yellow, and blue color can be adjusted to adjust the color
temperature of the white light.
[0147] In FIG. 11D, an LED lamp 150-1, which is a variation of the
LED lamp 150 shown in FIG. 5A, utilizes blue LEDs and different
phosphors to generate light of different colors other than blue,
and utilizes ultraviolet LEDs and blue phosphors to generate blue
light as shown in FIGS. 11A-11C. Further, the LED lamp 10 shown in
FIG. 3A can utilize blue LEDs and different phosphors to generate
light of different colors other than blue, and utilize ultraviolet
LEDs and blue phosphors to generate blue light as shown in FIGS.
11A-11C. For example, in FIG. 4, the LED string 112 can include
ultraviolet LEDs coated with blue phosphor, the LED string 114 can
include blue LEDs coated with phosphor P1, and the LED string 116
can include blue LEDs coated with phosphor P2. In a first
implementation, in the LED lamp 10 or 150-1, the phosphors P1 and
P2 to can be red and green, respectively. In a second
implementation, in the LED lamp 10 or 150-1, the phosphors P1 and
P2 can be reddish yellow and yellow, respectively. In a third
implementation, in the LED lamp 10 or 150-1, the phosphors P1 and
P2 can be red and yellow, respectively.
[0148] Referring now to FIGS. 12A and 12B, the blue LED string 112
shown in FIG. 4 can be implemented in different ways. For example,
in one implementation shown in FIG. 12A, the LED string 112 may
include ultraviolet LEDs coated with blue phosphor. In another
implementation shown in FIG. 12B, the LED string 112 may include
blue LEDs generating blue light having different wavelengths that
may be preselected and arranged in a predetermined order. For
example, blue LEDs producing blue light having wavelengths 470 nm,
475 nm, and 465 nm may be selected and arranged as shown. Other
wavelengths may be selected instead. The LEDs may be arranged in a
different order than shown. In this implementation, the blue
wavelengths average out to provide uniform blue light.
[0149] Referring now to FIG. 13, a method 500 for generating white
light according to the present disclosure is shown. At 502, control
determines the currents through the blue, green, and red LEDs to
produce white light. The green and red LEDs are blue LEDs coated
with green and red phosphors, respectively. The blue LEDs may not
be coated with a phosphor to convert blue light into a light of a
different color or may be coated with amber phosphor. At 504,
control determines if the blue LEDs are coated with amber phosphor.
At 506, if the blue LEDs are coated with amber phosphor, control
reduces current through the red LEDs in proportion to an amount of
red light produced by the blue LEDs coated with amber phosphor. At
508, control determines if a color temperature and/or brightness of
the white light is changed by a user. At 510, if the user changes
the color temperature and/or brightness of the white light, control
changes current through the blue, green, and red LEDs to produce
white light having the color temperature and/or brightness selected
by the user.
[0150] Referring now to FIG. 14, a method 600 for controlling a
color temperature of white light generated by an LED lamp according
to the present disclosure is shown. At 602, control supplies
currents to green, red, and blue LEDs to generate white light. The
green and red LEDs are blue LEDs coated with green and red
phosphors, respectively. The blue LEDs may not be coated with a
phosphor to convert blue light to a light of a different color or
may be coated with amber phosphor. At 604, control determines if a
user changed the color temperature and/or brightness of the white
light. At 606, if the user changed the color temperature and/or
brightness of the white light, control changes the proportion of
currents through the green, red, and blue LEDs based on the color
temperature and/or brightness selected by the user.
[0151] The foregoing description is merely illustrative in nature
and is in no way intended to limit the disclosure, its application,
or uses. For example, the wavelength values and ranges are
approximate and provided for illustrative purposes only and are not
intended to be limiting. Based on the disclosure and teachings
provided herein, a person of ordinary skill in the art would
appreciate the various other wavelength values and ranges that may
be used. The broad teachings of the disclosure can be implemented
in a variety of forms. Therefore, while this disclosure includes
particular examples, the true scope of the disclosure should not be
so limited since other modifications will become apparent upon a
study of the drawings, the specification, and the following claims.
For purposes of clarity, the same reference numbers will be used in
the drawings to identify similar elements. As used herein, the
phrase at least one of A, B, and C should be construed to mean a
logical (A or B or C), using a non-exclusive logical OR. It should
be understood that one or more steps within a method may be
executed in different order (or concurrently) without altering the
principles of the present disclosure.
[0152] As used herein, the term module may refer to, be part of, or
include an Application Specific Integrated Circuit (ASIC); a
discrete circuit; an integrated circuit; a combinational logic
circuit; a field programmable gate array (FPGA); a processor
(shared, dedicated, or group) that executes code; other suitable
hardware components that provide the described functionality; or a
combination of some or all of the above, such as in a
system-on-chip. The term module may include memory (shared,
dedicated, or group) that stores code executed by the
processor.
[0153] The term code, as used above, may include software,
firmware, and/or microcode, and may refer to programs, routines,
functions, classes, and/or objects. The term shared, as used above,
means that some or all code from multiple modules may be executed
using a single (shared) processor. In addition, some or all code
from multiple modules may be stored by a single (shared) memory.
The term group, as used above, means that some or all code from a
single module may be executed using a group of processors. In
addition, some or all code from a single module may be stored using
a group of memories.
[0154] The apparatuses and methods described herein may be
partially or fully implemented by one or more computer programs
executed by one or more processors. The computer programs include
processor-executable instructions that are stored on at least one
non-transitory tangible computer readable medium. The computer
programs may also include and/or rely on stored data. Non-limiting
examples of the non-transitory tangible computer readable medium
include nonvolatile memory, volatile memory, magnetic storage, and
optical storage.
* * * * *